Reduced energy welding system and method

ABSTRACT

A welding regime may implements cyclic short circuits under a closed loop voltage control approach. Upon clearing or imminent clearing of the short circuit, a current recess is implemented. The current recess reduces the current that would otherwise be applied to the weld, resulting in multiple benefits. The recess may be implemented by suspending voltage command signals. Following the current recess, normal control is resumed with the then-current voltage command.

BACKGROUND

The invention relates generally to welders, and more particularly to awelder configured to perform a welding operation in which a waveform isapplied to welding wire as the wire is advanced from a welding torch.

A wide range of welding systems and welding control regimes have beenimplemented for various purposes. A number of continuous weldingoperations are known, such as gas metal arc welding (GMAW), flux coredarc welding (FCAW) and so forth. Certain of these are sometimes referredto as metal inert gas (MIG) techniques. In general, they allow forformation of a continuing weld bead by feeding welding wire to a weldingtorch where an arc is established between the welding wire and aworkpiece to be welded. Electrical power is applied to the welding wireand a circuit is completed through the workpiece to sustain the arc thatmelts the wire and the workpiece to form the desired weld.

Advanced forms of MIG welding are based upon generation of power in thewelding power supply. That is, various regimes may be carried out inwhich current and/or voltage waveforms are commanded by the power supplycontrol circuitry to regulate the formation and deposition of metaldroplets from the welding wire, to sustain a desired heating and coolingprofile of the weld pool, to control shorting between the wire and theweld pool, and so forth.

While very effective in many applications, such regimes may be subjectto drawbacks. For example, depending upon the transfer mode, theprocesses may either limit travel speed, create excessive spatter(requiring timely cleanup of welded workpieces), provide less thanoptimal penetration, or any combination of these and other effects.Moreover, certain processes, such as ones operating in a spray mode ofmaterial transfer, may run excessively hot for particular applications.Others, such as short circuit processes, may run cooler, but may againproduce spatter and other unwanted weld effects.

Moreover, in certain welding situations and with certain weldingelectrodes, welding processes that are trained to implement cyclic shortcircuits between the electrode and the workpiece may add excessiveenergy to the weld. In short circuit processes, while short circuits areintended between the electrode and the workpiece, the behavior of thesystem during and following the short circuits may be key to ensuring asmooth process, improving weld characteristics, reducing energy input,and so forth.

There is a need, therefore, for improved welding strategies that allowfor welding in waveform regimes while improving weld quality and systemperformance.

BRIEF DESCRIPTION

The present invention provides welding systems designed to respond tosuch needs. In accordance with an exemplary implementation, a weldingsystem comprises power circuitry configured to convert incoming powerfrom a source to welding power, and control circuitry coupled to thepower circuitry and configured to implement a control regime to controlthe welding power output by the power circuitry in a welding operation.The control regime comprises closed loop control of voltage, detectionof a predetermined rate of change of a welding parameter, suspension ofclosed loop control of voltage and implementation of a current recess,followed by resumption of closed loop control of voltage.

The invention also provides methods for welding, such as, in accordancewith one aspect, implementing a voltage closed loop control of weldingpower in a welding regime, monitoring welding power parameters,identifying a rate of change of at least one welding power parameter,suspending voltage closed loop control of the welding power upondetermination that the rate of change of the at least one welding powerparameter has reached or exceeded a threshold to create a currentrecess, and resuming voltage closed loop control of welding powerfollowing the current recess.

DRAWINGS

FIG. 1 is a diagrammatical representation of an exemplary MIG weldingsystem illustrating a power supply coupled to a wire feeder forperforming welding operations in accordance with aspects of the presenttechniques;

FIG. 2 is a diagrammatical representation of exemplary control circuitrycomponents for a welding power supply of the type shown in FIG. 1;

FIG. 3 is a graphical representation of an exemplary waveform for shortcircuit welding in accordance with the present techniques; and

FIG. 4 is a flow chart illustrating certain control logic inimplementing the welding regime of FIG. 3.

DETAILED DESCRIPTION

Turning now to the drawings, and referring first to FIG. 1, an exemplarywelding system is illustrated as including a power supply 10 and a wirefeeder 12 coupled to one another via conductors or conduits 14. In theillustrated embodiment the power supply 10 is separate from the wirefeeder 12, such that the wire feeder may be positioned at some distancefrom the power supply near a welding location. However, it should beunderstood that the wire feeder, in some implementations, may beintegral with the power supply. In such cases, the conduits 14 would beinternal to the system. In embodiments in which the wire feeder isseparate from the power supply, terminals are typically provided on thepower supply and on the wire feeder to allow the conductors or conduitsto be coupled to the systems so as to allow for power and gas to beprovided to the wire feeder from the power supply, and to allow data tobe exchanged between the two devices.

The system is designed to provide wire, power and shielding gas to awelding torch 16. As will be appreciated by those skilled in the art,the welding torch may be of many different types, and typically allowsfor the feed of a welding wire and gas to a location adjacent to aworkpiece 18 where a weld is to be formed to join two or more pieces ofmetal. A second conductor is typically run to the welding workpiece soas to complete an electrical circuit between the power supply and theworkpiece.

The system is designed to allow for weld settings to be selected by theoperator, particularly via an operator interface 20 provided on thepower supply. The operator interface will typically be incorporated intoa front faceplate of the power supply, and may allow for selection ofsettings such as the weld process, the type of wire to be used, voltageand current settings, and so forth. In particular, the system isdesigned to allow for MIG welding with various steels, aluminums, orother welding wire that is channeled through the torch. These weldsettings are communicated to control circuitry 22 within the powersupply. The system may be particularly adapted to implement weldingregimes designed for certain electrode types, and where desired thesemay be selected via the operator interface.

The control circuitry, described in greater detail below, operates tocontrol generation of welding power output that is applied to thewelding wire for carrying out the desired welding operation. In certainpresently contemplated embodiments, for example, the control circuitrymay be adapted to regulate a short circuit MIG welding regime that makesand breaks short circuits between the welding electrode and theworkpiece while reducing energy into the weld by selectivelyimplementing a “gap” in a current (or voltage) waveform. In “shortcircuit” modes, droplets of molten material form on the welding wireunder the influence of heating by the welding arc, and these areperiodically transferred to the weld pool by contact or short circuitsbetween the wire and droplets and the weld pool. “Short circuit welding”or “short circuit MIG welding” refers to techniques in which a powerwaveform is generated, such as to control deposition of droplets ofmetal into the progressing weld puddle. In a particular embodiment ofthe invention, a specialized welding regime may be implemented in whichwaveforms and control signals are generated that have characteristics ofconventional short circuit welding techniques, while specifically andstrategically reducing energy input. It should be noted that while thepresent disclosure focuses primarily on short circuit welding regimes,the techniques disclosed may also be used with certain pulsed weldingregimes in which short circuits may or may not be intentionally created.

The control circuitry is thus coupled to power conversion circuitry 24.This power conversion circuitry is adapted to create the output power,such as waveforms that will ultimately be applied to the welding wire atthe torch. Various power conversion circuits may be employed, includingchoppers, boost circuitry, buck circuitry, inverters, converters, and soforth. The configuration of such circuitry may be of types generallyknown in the art in and of itself. The power conversion circuitry 24 iscoupled to a source of electrical power as indicated by arrow 26. Thepower applied to the power conversion circuitry 24 may originate in thepower grid, although other sources of power may also be used, such aspower generated by an engine-driven generator, batteries, fuel cells orother alternative sources. Finally, the power supply illustrated in FIG.1 includes interface circuitry 28 designed to allow the controlcircuitry 22 to exchange signals with the wire feeder 12.

The wire feeder 12 includes complimentary interface circuitry 30 that iscoupled to the interface circuitry 28. In some embodiments, multi-pininterfaces may be provided on both components and a multi-conductorcable run between the interface circuitry to allow for such informationas wire feed speeds, processes, selected currents, voltages or powerlevels, and so forth to be set on either the power supply 10, the wirefeeder 12, or both.

The wire feeder 12 also includes control circuitry 32 coupled to theinterface circuitry 30. As described more fully below, the controlcircuitry 32 allows for wire feed speeds to be controlled in accordancewith operator selections, and permits these settings to be fed back tothe power supply via the interface circuitry. The control circuitry 32is coupled to an operator interface 34 on the wire feeder that allowsselection of one or more welding parameters, particularly wire feedspeed. The operator interface may also allow for selection of such weldparameters as the process, the type of wire utilized, current, voltageor power settings, and so forth. The control circuitry 32 is alsocoupled to gas control valving 36 which regulates the flow of shieldinggas to the torch. In general, such gas is provided at the time ofwelding, and may be turned on immediately preceding the weld and for ashort time following the weld. The gas applied to the gas controlvalving 36 is typically provided in the form of pressurized bottles, asrepresented by reference numeral 38.

The wire feeder 12 includes components for feeding wire to the weldingtorch and thereby to the welding application, under the control ofcontrol circuitry 36. For example, one or more spools of welding wire 40are housed in the wire feeder. Welding wire 42 is unspooled from thespools and is progressively fed to the torch. The spool may beassociated with a clutch 44 that disengages the spool when wire is to befed to the torch. The clutch may also be regulated to maintain a minimumfriction level to avoid free spinning of the spool. A feed motor 46 isprovided that engages with feed rollers 48 to push wire from the wirefeeder towards the torch. In practice, one of the rollers 48 ismechanically coupled to the motor and is rotated by the motor to drivethe wire from the wire feeder, while the mating roller is biased towardsthe wire to maintain good contact between the two rollers and the wire.Some systems may include multiple rollers of this type. Finally, atachometer 50 may be provided for detecting the speed of the motor 46,the rollers 48, or any other associated component so as to provide anindication of the actual wire feed speed. Signals from the tachometerare fed back to the control circuitry 36, such as for calibration asdescribed below.

It should be noted that other system arrangements and input schemes mayalso be implemented. For example, the welding wire may be fed from abulk storage container (e.g., a drum) or from one or more spools outsideof the wire feeder. Similarly, the wire may be fed from a “spool gun” inwhich the spool is mounted on or near the welding torch. As notedherein, the wire feed speed settings may be input via the operator input34 on the wire feeder or on the operator interface 20 of the powersupply, or both. In systems having wire feed speed adjustments on thewelding torch, this may be the input used for the setting.

Power from the power supply is applied to the wire, typically by meansof a welding cable 52 in a conventional manner. Similarly, shielding gasis fed through the wire feeder and the welding cable 52. During weldingoperations, the wire is advanced through the welding cable jackettowards the torch 16. Within the torch, an additional pull motor 54 maybe provided with an associated drive roller, particularly for aluminumalloy welding wires. The motor 54 is regulated to provide the desiredwire feed speed as described more fully below. A trigger switch 56 onthe torch provides a signal that is fed back to the wire feeder andtherefrom back to the power supply to enable the welding process to bestarted and stopped by the operator. That is, upon depression of thetrigger switch, gas flow is begun, wire is advanced, power is applied tothe welding cable 52 and through the torch to the advancing weldingwire. These processes are also described in greater detail below.Finally, a workpiece cable and clamp 58 allow for closing an electricalcircuit from the power supply through the welding torch, the electrode(wire), and the workpiece for maintaining the welding arc duringoperation.

It should be noted throughout the present discussion that while the wirefeed speed may be “set” by the operator, the actual speed commanded bythe control circuitry will typically vary during welding for manyreasons. For example, automated algorithms for “run in” (initial feed ofwire for arc initiation) may use speeds derived from the set speed.Similarly, various ramped increases and decreases in wire feed speed maybe commanded during welding. Other welding processes may call for“cratering” phases in which wire feed speed is altered to filldepressions following a weld. Still further, in certain welding regimes,the wire feed speed may be altered periodically or cyclically.

FIG. 2 illustrates an exemplary embodiment for the control circuitrydesigned to function in a system of the type illustrated in FIG. 1. Theoverall circuitry, designated here by reference numeral 60, includes theoperator interface 20 discussed above and interface circuitry 28 forcommunication of parameters to and from downstream components such as awirefeeder, a welding torch, and various sensors and/or actuators. Thecircuitry includes processing circuitry 62 which itself may comprise oneor more application-specific or general purpose processors, designed tocarry out welding regimes, make computations for waveforms implementedin welding regimes, and so forth. The processing circuitry is associatedwith driver circuitry 64 which converts control signals from theprocessing to drive signals that are applied to power electronicswitches of the power conversion circuitry 24. In general, the drivercircuitry reacts to such control signals from the processing circuitryto allow the power conversion circuitry to generate controlled waveformsfor welding regimes of the type described in the present disclosure. Theprocessing circuitry 62 will also be associated with memory circuitry 66which may consist of one or more types of permanent and temporary datastorage, such as for providing the welding regimes implemented, storingwelding parameters, storing weld settings, storing error logs, and soforth. Sensors and/or actuators, designated generally by referencenumeral 68 may be interfaced with the processing circuitry via theinterface circuitry 28. In many systems, at least current and voltagesensors will be provided to allow for closed-loop control of the weldingpower control waveform as described below. Other sensors will typicallyallow for input of torch trigger signals, among many other signals thatmay be monitored and/or controlled by the processing circuitry. Hereagain, it should be noted that some of these parameters or weldingoperation aspects may be controlled by the wire feeder, or bycooperative control by the power supply and the wire feeder.

More complete descriptions of certain state machines for welding areprovided, for example, in U.S. Pat. No. 6,747,247, entitled“Welding-Type Power Supply With A State-Based Controller”, issued toHolverson et al. on Sep. 19, 2001; U.S. Pat. No. 7,002,103, entitled“Welding-Type Power Supply With A State-Based Controller”, issued toHolverson et al. on May 7, 2004; U.S. Pat. No. 7,307,240, entitled“Welding-Type Power Supply With A State-Based Controller”, issued toHolverson et al. on Feb. 3, 2006; and U.S. Pat. No. 6,670,579, entitled“Welding-Type System With Network And Multiple Level Messaging BetweenComponents”, issued to Davidson et al. on Sep. 19, 2001, all of whichare incorporated into the present disclosure by reference. A method forwelding utilizing voltage controlled loops is described in U.S. Pat. No.6,090,067, entitled “Method and Apparatus for Welding with CV Control”,issued on Jun. 21, 2005 to Davidson et al, which is incorporated intothe present disclosure by reference. Certain other welding techniquesare disclosed in U.S. Pat. No. 6,974,931, entitled “Method and Apparatusfor Pulse and Short Circuit Arc Welding”, issued on Dec. 13, 2005 toHolverson et al., and U.S. Pat. No. 6,933,466, entitled “Method andApparatus for Arc Welding with Wire Heat Control”, issued on Aug. 23,2005 to Hutchison et al., both of which are incorporated into thepresent disclosure by reference. Further, techniques for predictingshort circuit clearing in welding processes are disclosed in U.S. patentpublication no. 20120061362, entitled “Method and Apparatus for Weldingwith Short Clearing Prediction”, filed on Nov. 12, 2010 by Davidson etal, which is also incorporated into the present disclosure by reference.

FIG. 3 generally illustrates an exemplary waveform for a weldingtechnique in which molten metal from the welding electrode istransferred to the workpiece by a modified short circuit weldingtechnique. In particular, the technique comprises a welding regime inwhich the welding power supply control circuitry controls the conversionof incoming power to welding power in a GMAW or similar process. Theprocess is essentially “constant voltage” (“CV”), which in fact entailssensing weld voltage and closing a control loop on voltage so thatcommand signals can be generated that are applied to the powerconversion circuitry to have the weld voltage follow a desired profile,reach desired levels, respond in desired ways, and so forth. Whilecontrol loops can also be closed on other parameters, such as weldcurrent, the weld current will typically respond to the commandedvoltage under the dynamics of the process (e.g., wire electrode advance,state of the arc, travel speed, and so forth).

In the new process, a current recess is created that may aid the processin a number of ways. Although the process is based on closed loopcontrol of voltage, the current recess may be produced by temporarilysuspending that control and allowing current to drop, then resuming thevoltage closed loop control. The drop in current will reduce the energyinput into the weld, allowing the weld to run cooler and quieter,reducing spatter, and allowing for a shorter arc and enhanced travelspeed. In fact, in a currently contemplated implementation, the weldingregime may be a “short circuit” process in which a short circuit iscreated, expected, or even forced in each cycle such that voltage willdrop considerably when the short circuit occurs, then rise sharply whenthe short circuit clears or begins to clear. It is at this patter pointthat the current recess is implemented.

As used herein, the term “current recess” refers to a significant andoperationally effective drop in current from levels that would prevailor result from otherwise continuing the closed loop voltage control. Theeffect of the recess can be clearly seen in waveform traces of weldcurrent (as discussed below in connection with FIG. 3), forming a gap ornoticeable drop in weld current during the recess period.

It should also be noted that the current recess technique may used witha variety of processes and process settings, including GMAW processes,FCAW processes, and so forth. The processes may be electrode positive aswell as electrode negative, or the polarity may be reversed during theprocess. In some cases, electrode negative (sometimes called “straightpolarity”) may be preferred so as to enhance removal of energy from thewelding arc.

FIG. 3 illustrates waveforms for a welding regime 70 that implements thecurrent recess technique disclosed. The figure shows 3 cycles of awelding process, with a current trace 72, a voltage trace 74, and a“trigger” trace 76, all over time 78. Again, in the presentlycontemplated embodiment, the entire process is based on the controlcircuitry implementing a welding regime via closed loop control of weldvoltage. Moreover, in this short circuit welding process (or somemodified short circuit process), the voltage trace can be expected toshow a sudden drop in voltage as the molten end of the welding electrodeshorts (i.e., extends to, touches, or is bridged by molten material) tothe workpiece, or in most cases, to the progressing weld puddle. Thus,at time 80, the voltage trace 74 can be seen to drop suddenly, asindicated at reference numeral 82. At this time, the current will beexpected to increase from a lower level 84.

The trigger trace 76 represents a parameter that the control circuitrymonitors, or in most cases may calculate, such as a first timederivative of weld voltage. Other triggering parameters may, of course,be used, such as a derivative of current, a higher derivative ofvoltage, a derivative of power, and so forth. As indicated by referencenumeral 86, then, when the voltage drops due to the short circuit, therate of change of voltage will show a sudden drop as well. In thepresently contemplated embodiment, the control circuitry continues toregulate the voltage in a closed loop manner during this time, and at alater time 88 a sudden rise in voltage will be observed due to theclearing or imminent clearing of the short circuit. The trigger tracewill exhibit a sudden spike, as indicated by reference numeral 90 due tothe much higher rate of increase in the voltage waveform at this time.

In this embodiment, the sudden spike in the rate of change of weldvoltage is used as a trigger to implement the current recess. Returningto the current trace, as the short circuit occurs, the current tracewill rise, as indicated by reference numeral 92. Ordinarily, without thecurrent recess, the current trace in this particular welding regimewould have a sawtooth appearance over time, as illustrated. However,here the current recess 94 is implemented to reduce the current andenergy input into the weld. In particular, the spike in the voltage rateof change causes the control circuitry to suspend closed loop controlbased on voltage (that is, in the current implementation, the commandsignals are stopped), and the current is allowed to drop as shown inFIG. 3. The current recess may be implemented in a number of ways, andthese may determine both the onset of the recess as well as thetermination or duration. In a currently contemplated embodiment, theduration of the current recess is programmable, and may be of a fixedduration (set in advance). In some cases, hard fixed durations, variabledurations, operator-adjustable durations, or algorithmically computedrecess termination points may be implemented. In the currentimplementation, the current recess may be between about 0.1 and 2 ms,and particularly between about 0.4 and 1 ms, for example, as indicatedby reference numeral 96.

Following the current recess, normal voltage closed loop control isresumed. This will cause the voltage waveform to resume peaks and dropsas the arc is powered and the next short circuit is developed. Thecurrent trace will exhibit a decline in current, as shown by referencenumeral 98 as the electrode and weld pool part. It should be noted,however, that in this current implementation, the voltage commands thatwould have been implemented are still computed, any running averages ofvoltage are still computed, internal “inductances” are still implementedor computed, and so forth. The current recess merely interruptsapplication of these commands to the power conversion circuitry. Thus,after the current recess, the current trace resumes the sawtooth profile(in this case), and the recess appears as a gap “cut from” each tooth.It will be apparent to those skilled in the art, however, that somealteration in the voltage waveform itself is likely as compared tocontrol without the current recess, owing to the effect of removal ofthe voltage command, and the resulting change in voltage or voltagedynamics during the current recess.

FIG. 4 illustrates exemplary control logic 100 for implementing acurrently contemplated short circuit welding regime utilizing a currentrecess. Of course, the actual code or even the pseudocode for thewelding regime will include many more details, but that are generallybeyond the scope of this disclosure, and that are well within the ambitof those skilled in this art. The logic begins at step 102 where voltageis applied to the welding electrode to create and maintain the weldingarc between the electrode and the workpiece (or generally with the weldpuddle). At step 104, the voltage is controlled in a closed loop manner,typically by reference to a design voltage and a sensed weld voltage. Asindicated at step 106, the system continuously monitors for thetriggering event to initiate the current recess, which in this case isthe sudden rise in the first derivative of voltage (although one or moreother triggers may be referenced). In general, the triggering event heremay be considered as any indication that the short circuit between thewelding electrode and the weld puddle has cleared or will clear. Theprocess continues in this way until the triggering event is detected.

Once the triggering event is detected, closed loop voltage control ofwelding power is suspended to create the desired current recess, asindicated by reference numeral 108. At the same time, while to createthe current recess, at least in a currently contemplated embodiment, thevoltage commands are simply suspended, as noted above, the controlcircuitry nevertheless continues to compute the command signals thatwould have been applied to the conversion circuitry but for the currentrecess, as indicated at step 110. This allows for seamlessly taking upcontrol following the current recess. The system ultimately determinesthat the current recess is complete, as indicated by step 112, and oncecomplete, resumes normal voltage closed loop control with thethen-current voltage command signal. This process is repeated forsubsequent cycles of the short circuit regime.

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

1. A welding system comprising: power circuitry configured to convertincoming power from a source to welding power; control circuitry coupledto the power circuitry and configured to implement a control regime tocontrol the welding power output by the power circuitry in a weldingoperation, the control regime comprising closed loop control of voltage,detection of a predetermined rate of change of a welding parameter,suspension of closed loop control of voltage and implementation of acurrent recess, followed by resumption of closed loop control ofvoltage.
 2. The system of claim 1, wherein the power circuitry isconfigured to implement a gas metal arc welding process under thecontrol of the control circuitry, and wherein the system comprises awire feeder that receives the welding power and applies the weldingpower to a wire electrode advanced during the welding operation.
 3. Thesystem of claim 1, wherein the control circuitry is configured to detecta predetermined rate of change of welding voltage for suspension of theclosed loop control of voltage and the implementation of the currentrecess.
 4. The system of claim 1, wherein the current recess reducescurrent from a level that would result from continued closed loopcontrol of voltage.
 5. The system of claim 1, wherein the weldingoperation comprises an electrode positive regime.
 6. The system of claim1, wherein the welding operation comprises an electrode negative regime.7. The system of claim 1, wherein the current recess is of apredetermined duration.
 8. The system of claim 1, wherein during thecurrent recess the control circuitry is configured to continue tocompute command signals that would have been applied to the powercircuitry but for the current recess, but not to apply the computedcommand signals to the power circuitry during the current recess.
 9. Thesystem of claim 8, wherein following termination of the current recess,the control circuitry applies then-current command signals to the powercircuitry continuing as if the current recess had not occurred.
 10. Amethod comprising: implementing a voltage closed loop control of weldingpower in a welding regime; monitoring welding power parameters;identifying a rate of change of at least one welding power parameter;suspending voltage closed loop control of the welding power upondetermination that the rate of change of the at least one welding powerparameter has reached or exceeded a threshold to create a currentrecess; and resuming voltage closed loop control of welding powerfollowing the current recess.
 11. The method of claim 10, comprising,during the current recess, continuing to compute command signals thatwould have been used to control the welding power but for the currentrecess.
 12. The method of claim 11, comprising, following termination ofthe current recess, the control circuitry utilizing the then-currentcommand signals to control the power circuitry.
 13. The method of claim10, wherein the rate of change comprises a first time derivative of weldvoltage.
 14. The method of claim 10, wherein during the welding regimethe weld current comprises a generally saw-tooth profile versus time,and wherein the current recess produces a current gap formed in eachtooth of the saw-tooth profile.
 15. The method of claim 10, wherein thewelding operation comprises an electrode positive regime.
 16. The systemof claim 10, wherein the welding operation comprises an electrodenegative regime.
 17. The system of claim 10, wherein the current recessis of a predetermined duration.
 18. A method comprising: implementing avoltage closed loop control of welding power in a welding regime;monitoring weld voltage; identifying a rate of change of weld voltage toidentify when rate of change of weld voltage exceeds a predeterminedthreshold; based upon the weld voltage parameter exceeding thepredetermined threshold, suspending voltage closed loop control of thewelding power to create a current recess; and resuming voltage closedloop control of welding power following the current recess.
 19. Themethod of claim 18, wherein during the welding regime the weld currentcomprises a generally saw-tooth profile versus time, and wherein thecurrent recess produces a current gap formed in each tooth of thesaw-tooth profile.
 20. The system of claim 18, wherein the currentrecess is of a predetermined duration.